Ayano Nakakouji is a teenage girl characterized by long, waist-length blonde or orange hair, typically styled with blunt bangs and curly textures, often adorned by a bow or hair ribbon. Her eyes are usually brown but sometimes appear yellow across different media portrayals.

She lives as the daughter of a mansion-dwelling client who employs a private detective for protection. The mansion staff includes butler Shibata, janitor Imada, live-in maid Nozomi, and home tutor Kaoru. Ayano's initial presence centers on her status within this isolated setting.

As events unfold, Ayano develops a profound psychological fixation on the detective, Kido, believing him the reincarnation of her former master. She actively pursues becoming his "pleasure doll," driven by a desire for submission intertwined with a twisted devotion. This conviction fuels intense jealousy toward other women in the mansion, particularly maid Nozomi and Kido's partner Mei, revealing possessive tendencies and instability.

Her interactions further include a tendency to address Kido as "father," though the reason for this designation is not elaborated.